Although the standard home washing machine has been developed and perfected to a high degree, large-capacity machines such as used in commercial laundries, hospitals, collectives, and the like have remained relatively crude. The most recent development in such commercial washing machines has been so-called continuous washers which are formed with an elongated housing having an input end and an outlet end. Laundry may be continuously introduced into the input end and is continuously expelled from the output end. Such an arrangement, referred to as a washing tunnel, is internally subdivided into several zones respectively responsible for the soaking, prewashing, washing, and rinsing of the articles introduced into the inlet end. In each zone the water is maintained at a predetermined temperature and various washing products are added. As a rule the water is circulated from the outlet end back toward the input end.
In the commonest type of such devices inside the longitudinally elongated cylindrical housing there is provided a similarly shaped drum. The entire arrangement is tipped slightly toward the output end so that as the internal drum is rotated the clothing and the like within it is tumbled and slowly progresses toward the outlet end. With such an arrangement some articles are washed much more thoroughly than others. In addition the simple tumbling action caused by continuous rotation of the treatment drum is not on the whole as effective as an agitation or oscillation of this drum would be.
Attempts have been made to overcome these disadvantages by providing a central compartmented drum in the housing forming a spiral with a succession of flat partitions alternating with helical ones. In such an arrangement the different laundry articles advance at approximately the same speed and do not get mixed together. Such a system has, however, the considerable disadvantage that the central drum is extremely expensive and difficult to manufacture. It must be delivered to the site as a single unit and does not allow the type of washing operation to be altered by addition or removal of stages. In addition it is necessary that the articles in each compartment be subjected to exactly the same type of tumbling or agitating movement so that, for instance, a still-standing presoak cannot be carried out at the same time as a tumbling or oscillating wash cycle. In some arrangements (see German Pat. No. 1,948,045 ) the drum is rotated continuously in one direction whereas in other systems (see U.S. Pat. No. 3,103,802) the drum is oscillated back and forth about its axis. Continuous rotation in the same direction or tumbling has been found to be relatively ineffective for thorough washing, and oscillation through less than 270.degree. has similarly been found to be of very reduced effectiveness.
So-called modular systems have been described (see British Pat. No. 516,772 and U.S. Pat. No. 2,056,803 ). In such systems the separate sections of the drum are nonetheless constrained to rotate together once the assembly is installed so that once again a still-standing soak is impossible during a washing operation in the same machine. Furthermore the laundry must be transferred from each chamber to the next chamber simultaneously so that a very large drive motor must be employed and heavy-duty power circuits installed to handle the load.
It is also known to provide vanes within the drum of a washing machine (see French Pat. No. 1,226,393, German Pat. No. 1,290,909, and U.S. Pat. Nos. 3,084,531 and 3,364,588). In such a system the vane is built such that rotation of the drum in one direction tumbles the laundry within the drum, but rotation in the opposite direction displaces it axially to unload the drum. Such a system nonetheless relies on the above-described ineffective tumbling effect. In addition such an arrangement frequently causes a considerable quantity of water to be dumped out of the drum when it is reversed.